COD-LIVER OIL 43I
are coloured pale yellow to brownish red and have a more or less unpleasant
odour. With alcoholic potash they mostly give brown soaps ; they contain
small quantities of unsaponifiable substances (0-5-2%). When dissolved
in carbon disulphide and treated with a little cone, sulphuric acid, they
give a reddish-brown coloration with no trace of violet (see Cod-liver Oil).
They give the general reactions for marine animal oils described above
and their characters are given later in Table XLVII I.
Their analysis includes the following :
1. Water, Impurities, Acidity.—These are determined as in General
Methods, i and 7.
2. Distinction between Fish Oils and Blubber Oils.—With pure
oil of one kind or the other, the iodine and Maumene numbers are sufficient
to determine if it is fish oil or whale (or seal) oil (see Table XLVIII). Mix-
tures of the two types of oil cannot be identified.
The reaction with carbon disulphide and sulphuric acid serves to dis-
tinguish fish and blubber oils from liver-oils (see following article).
3. Detection of Impurities :
(a) MINERAL AND RESIN OILS. These are detected by saponifying the
oil (50-100 c.c.) and extracting and examining the unsaponifiable matter
as indicated in General Methods, 19.
(6) VEGETABLE OILS. These are detected by the digitonin test for
phytosterol (see Hog's Fat). Cottonseed and sesame oil may also be iden-
tified by means of their special colour reactions, provided that the oil is not
too much coloured.
This is obtained from the liver of Gadus monhua and of other allied fish
of the Northern Atlantic. According to its purity and colour it is divided
into : white (medicinal, superior), which is clear, of pale or straw yellow
colour, almost odourless and almost tasteless ; pale, which is clear, reddish-
yellow, and with a marked fishy odour and taste ; red or brown, which is more
or less turbid and brownish-red and with an unpleasant fishy odour and
It dissolves slightly in alcohol, but easily in ether, benzene or other
ordinary fat solvent. It contains small quantities of unsaponifiable sub-
stances (mainly cholesterol) : 0-3-2% in pale oils and up to about 8% in
crude brown ones.
Further it contains traces of iodine in organic combination (o-oco2-
0-04%). This is not extractable by solvents or by mere saponification, but
is detected only by saponifying the oil, adding a little nitre to the soap,
evaporating to dryness, incinerating and carefully calcining and testing
the ash for iodine in the usual way.
It gives the general reactions of marine animal oils described above,
and its characters and those of the livers of other fish are given in Table
XLVIII. The determinations to be made are :
1. The Special Reaction for this oil, but common to all others from
fish-livers, is as follows : A drop of the oil is dissolved in 2 c.c. of carbont free from acid and filtered through